This patient has porphyria cutanea tarda (PCT). PCT is a rare skin disease that typically occurs in the setting of underlying liver disease, which in this patient is likely due to heavy alcohol use. It may also develop in patients with chronic hepatitis C infection and hemochromatosis. PCT is caused by decreased activity of hepatic uroporphyrinogen decarboxylase, an enzyme in the heme biosynthesis pathway that leads to accumulation of porphyrins in the tissues. Only 20% of cases of PCT are due to inherited enzyme mutations, the remainder is acquired. The acquired forms appear to be related to increased oxidative stress in hepatocytes, possibly associated with iron deposition, although the exact mechanisms of decreased enzyme activity have not been elucidated. Patients with PCT often have darkening of the skin, hypertrichosis, and fragility of the skin, particularly in sun-exposed and frequently traumatized areas, such as the dorsal hands. Numerous scars and small milia (tiny proteinaceous cysts) are often seen on the dorsal hands; intact blisters are rare, but often exist transiently before being spontaneously ruptured following mild trauma.

Allergic contact dermatitis may lead to blisters, but not scarring or milia, and there is no history to suggest an environmental trigger in this patient. The lesions of contact dermatitis typically will be sharply demarcated and geometric in appearance, corresponding to the area affected by the causative agent.

Bullous lupus erythematosus is a rare form of cutaneus lupus in which patients develop small blisters within and in addition to their other cutaneous lupus lesions; the blisters are generally small and often rupture with some residual dyspigmentation and scarring. Signs of systemic lupus erythematosus should be present when making a diagnosis of bullous lupus erythematosus.

Bullous pemphigoid is an autoimmune blistering disease common in the elderly that presents with urticarial plaques and tense, intact bullae; there is no association with liver disease.